In many surgical procedures, including joint replacement such as Total Hip Arthroplasty (THA), achieving precise positioning of tools and implants with respect to a patient's anatomy is critical for successful outcomes. FIG. 1 illustrates a pre-operative 100 and post operative 102 hip joint, along with a coordinate frame defining various directions 104. The post-operative hip joint is composed of a femoral component 106 and an acetabular component 108. In one THA technique, the hip joint is exposed and dislocated. The acetabulum and the femur are prepared for receiving implants. Typically, a cup prosthesis is to be implanted in acetabulum requiring alignment of the cup with respect to the patient's anatomy. Trial femoral prosthetics—available in various sizes to facilitate intra-operative adjustment—may be implanted to assess the correct final femoral implant size. The fit and sizing of the joint may be iteratively assessed and a final prosthetic hip joint (106 and 108) implanted.
Positioning prosthetic implants relative to the patient's anatomy may involve numerous challenges such as selecting the correct implant geometry and altering the patient's bony anatomy (e.g. reaming, osteotomy, etc.), among others. Some important goals for a successful THA include: proper alignment of the acetabular cup; restoration or correction of leg length and offset; restoration of hip center-of-rotation (COR); and stability of new hip joint. The concept of leg length and offset change seems simple at first; however, it is a complex clinical and geometrical problem. The surgeon is often required to make various accurate assessments of leg length and offset intra-operatively.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.